Means for minimizing incomplete securing of flush latches



United States Patent [72] Inventor Lloyd Richard Poe Primary Exanziner-Marvin A. Champion Beverly Bin C liforni Assistant Examiner- Robert L. Wolfe 21 Appl. No. 752,340 Alwmeyhyoh & y [22] Filed Aug. 13, 1968 [45] Patented Nov. 24, 1970 [73] Assignee Hartwell Corporation Los f cahforfua ABSTRACT: A means for minimizing incomplete fastening of a corpomno of Cahforma flush latches of the type disclosed in US. Pat. Nos. 2,476,268 and 2,639,178; as well as the types of flush latches disclosed MEANS FOR MINIMIZING INCOMPLETE int liShPat Nos. 2,72 l ,750, 2.7121955 andd2,i33,582, tthese SECURING F FLUSH LATCHES a c es avmg In common a trigger ever an a eeper su ect to forces exerted by two springs, the lever and keeper incor- 15 Claims, 15 Drawing Figs. I

porating mutually engaging surfaces which move past a mu- [52] US. Cl 292/113 tually abutting condition on pivotal movement of the trigger [51] E 1 /1 lever at which position forces are balanced and the latch is [50] held in a partially secured condition; more particularly, the t .means for minimizing this condition; involves the use of two I 341-11129 springs in which the force of one is sufficiently greater than the other that the region in which such partially secured con- [56] References dition can occur is minimized, and the frictional contact UNITED TATE PAT NT between the mutually engaging surfaces is also minimized; to 2,158,983 5/1939 Knoll 292/174 the end that the probability of a p so remote and the 2 721 750 10/1955 R di et l 292/139 condition of balance so unstable that, for practical purposes, 2,899,227 8/1959 Gschwend 292/163 such partially secured condition is avoided.

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v s /o 26/ Q /6 38 26 Patented Nov. 24, 1970 Sheet 2 of 3 m m 0 W s 1 V0 H m N W R m m I D 9 i W F 0 L Y. l B

NO LOAD Patented Nov. 24, 1970 Sheet 3 .INVENTOR.

LLOYD RICHARD POE M m F 'ATTORNEY ing surface,

t MEANS FOR MINIMIZING INCOMPLETE srscumnc or FLUSH LATCHES BACKGROUND ANI) SUMMARY OF THE INVENTION the mechanic is present to note the resulting closed condition,

I or to refasten the latch ifthe latch is open,

while the opposite end of the bolt handle lever engages a keeper or margin-of an opening closed by a door on which the latch is mounted. Intermediate portions of both levers are mounted essentially flush with a surrounding surface.

By reason of the fact that theexposed parts of the latch could be formed so as to be essentially flush with a surroundand thus offer minimal wind resistance, the flush latch has been used extensively on aircraft, sometimes many on a single aircraft, for inspection panels and access'doors.

It was quickly realized that a rigid and often redundant inspection system was required to be sure the flush latches were fully closed before flight for it was discovered that unless the mechanic was careful, he could cause the bolt handle and trigger levers to mutually engage and each lever hold the other in partially open position and with the bolt lever in engagement with its keeper so that the panel on which the latch was mounted was held in place, but in an unstable condition. Unless one examined the latch closely, this condition might not be observed. Then under conditions of vibration or when subjected to wind loads as developed, for example, on takeoff, the flush latch would open, causing the panel to fall off or be sucked into the aircraft to interfere with controls or cause damage. Particularly disastrous results can occur if the panel secured by the flush latch is in a position to be sucked into a jet engine as this could result inloss of the engine or even loss of the airplane.

The problem present in regard to the before mentioned type of flush latch applies also to the types of flush latches represented in U.S. Pat. Nos. 2,72l,750; 2,712,995 and 2,833,582. These latches differ, however, in that the functions of the bolt-handle lever are divided, there being a handle lever and a separate but connected bolt which may take several forms. Also, the trigger latch engages a fixed keeper pin in place of the bolt-handle lever; yet, the forces applied on the trigger lever in its relation to the keeper pin are essentially the same and are dependent on the forces exerted by a pair of springs as in the first-mentioned type'of flush latch.

The flush latches described in the above three patents are also used primarily in aircraft; however, they are usually of larger size than the previously mentioned type of latch and are used for access doors, cowling doors and the like; thus, the damage, ifone should open in flight, is substantial.

As indicated previously, the only solution heretofore has been a system of rigid inspection, which is complicated by the fact that a large number ofsuch panels and their flush latches are provided on each airplane, many of which are in places which are difficult to reach and to inspect.

The present invention solves this long standing and vexing problem by what may appear, after accomplishment, to be two superficial changes. First, the two springs which turn the bolthandle lever or the handle lever, depending upon which latch is involved, and the trigger lever are selected so that in the re gion of mutual engagement, in which an effective balanced force condition might occur, the directions and relative magnitudes ofthe torques exerted by the two springs minimize the area over which this can occur. Second, the frictional engagement between the mutually engaging parts is reduced to a minimum. The two factors spring torque and minimum friction are interrelated for the reason that if the friction is too high, the required spring force becomes excessive. However, by proper selection of these two factors, the parts, when so interengaged that each holds the other open, are in such unstable interengagement that they do not remain so engaged, but snap immediately to a latched or unlatched condition, while DESCRIPTION OF THE FIGURES FIG. 1 is a plan view of the type of flush latch disclosed'in U.S. Pat. Nos. 2,476,268 and 2,639,178; embodying the invention, indicating by broken lines, portions of the panel and surrounding frame.

FIG. 2 is an enlarged fragmentary view of the llush latch.

FIG. 3 is a further enlarged longitudinal sectional view thereof, taken through 3-3 of FIG. 1.

FIG. 4 is a fragmentary plan view, showing the retained end ofthe bolt lever.

FIG. 5 is a fragmentary sectional view, similar to FIG. 2, showing the interengaging portions of the bolt lever and trigger'lever, with the springs omitted, illustrating a modified form ofthe flush latch.

FIG. 6 is a similar fragmentary sectional view, showing a further modified form of the flush latch.

FIG. 7 is another fragmentary sectional view, showing adjacent portions of the bolt lever and the trigger lever, and illustrating a further modified construction.

FIG. 8 is a diagrammatic longitudinal sectional view, corbottom view or inside responding to FIG. 3, showing the isolated bolt lever and trigger lever in their fully latched position.

FIG. 9 is a fragmentary diagrammatical view, showing the trigger lever and the engaging portion of the bolt lever in their latched relation, and indicating the forces'reacting to the bolt lever and trigger lever spring loads.

FIG. I0 is a fragmentary diagrammatical view, similar to FIG. 9, showing the engaging portion of the bolt lever at the tip of the trigger lever.

FIG. 11 is a further enlarged fragmentary diagrammatical view, indicating the trigger lever and the engaging portion of the boltlever, with particular reference to a random angle between a relative, fully latched condition and an essentially disengaged condition.

FIG. 12 is a fragmentary essentially diagrammatical view of the type I of latch more fully disclosed in U.S. Pat. No.

2,721,750, showing the mathematical relation of the essential elements thereof for comparison with FIG. 8.

FIG. 13 is a fragmentary essentially diagrammatical view of the type of latch more fully disclosed in U.S. Pat. No. 2,712,955, also showing the mathematical relation of the essential elements thereof for comparison with FIG. 8.

FIGLM is a fragmentary essentially diagrammatical view of the type of latch more fully disclosed in U.S. Pat. No. 2,833,582, also showing the mathematical relation of the essential elements thereoffor comparison with FIG. 8.

FIG. 15 is a fragmentary-diagrammatical view of the trigger lever and the element engaged thereby corresponding to the area within circle '15 of FIGS. I2, 13 and 14', FIG. 15 corresponding to FIG. ,1 l.

The flush latch of the type shown in U.S. Pat. Nos. 2,476,268 and 2,639,178, includes a mounting plate 1, divided except for an end web 2 by a lever receiving slot 3. Bordering the slot adjacent the end of the plate remote from the end web 2 is an opposed pair of bolt lever journal flanges 4, and nearer the slot is a pair of opposed trigger lever journal flanges 5.

Fitted between the rately, a bolt and handle lever, which is channel shaped in cross section, thus forming side flanges 7, connected by a web. The web includes a flush portion 8 which is raised a predetermined distance above the surface of the mounting plate, de pending upon the thickness of the metal forming a panel or door under which the mounting plate I is positioned. The web continues from one end of the flush portion to form an inwardly sloping portion 9 which continues to form an inwardly offset latch engaging tab 10.

flanges 4 is a bolt lever 6; or, more accu- The side flanges 7 are provided with a pair of transversely alined apertures located under the juncture between the flush portion 8 and the sloping portion 9. The apertures receive a pivot pin 11, the ends of which extend through journal apertures provided in the pair of journal flanges 4.

A trigger lever 12 is provided which is likewise essentially channel-shaped in cross section and includes side flanges l3 and a web, the major portion of which forms a flush portion 14 adapted to occupy a position flush with the flush portion 8. One end of the flush portion 14 confronts the flush portion 8, whereas the opposite end is offset inwardly to form a tab 15 which underlies the end web 2. At its end opposite from the tab 15, the trigger lever is provided with extended ears 16 continuing from the side flanges 13 and offset longitudinally to a point a short distance under the confronting end of the bolt lever 6.

The ears 16 are provided with a pair of alined apertures which receive a pivot pin 17, the extremities of which project into journal openings provided in the trigger lever journal flanges 5.

The construction so far described may be considered as conventional, and is essentially the construction shown in the two patents mentioned in connection with the background of the invention.

In the exercise of the present invention, and referring particularly to FIGS. 1 through 4, the side flanges 7 are provided with extensions 18 which project under the adjacent end of the trigger lever 12. The extensions 18 receive therebetween a roller shaft 19 on which is mounted a roller 20 which bears against the underside of the flush portion 14 of the trigger lever 12, as shown in FIG. 3. In this construction, the roller constitutes the restrained portion or element of the bolt lever 6, whereas the overlying end 21 of the trigger lever 12 forms the retaining end or portion of the trigger lever.

The bolt lever 6 is provided with a bolt lever spring 22, having coils 23 wrapped about the pivot pin 11, and extended spring arms 24 and 25. The spring arms 24, which may be joined to form a loop, bear against the underside of the flush portion 8 of the bolt lever web, whereas the spring arms 25 extend over the pivot pin 17 and bear against this pivot pin so that the bolt lever spring 22 exerts a force tending to turn the bolt lever 6 in a counterclockwise direction, as viewed in FIG. 3.

The trigger lever 12 is provided with a spring 26, having coils 27 which wrap about the pivot pin 17. The coils are joined to a pair of extended spring arms 28 which may be joined at their extremities to form a loop. The other ends of the coils 27 terminate in hook elements 29 which fit over projections 30, extending from the journal flanges 5.

As will be brought out in more detail hereinafter, the roller 20 minimizes the friction incidental to relative movement of the retained and retaining ends of the bolt lever and trigger lever. When the roller 20 is in the position shown in FIG. 3 or nearly so, the bolt lever spring 22 acting on the roller tends to rotate the trigger lever 12 in a counterclockwise direction as viewed in FIG. 3, andthus tends to move or hold the flush portions 8 and 14 in flushed relation with the surrounding panel, designated P in FIG. 1, and cause the tab to engage the margin of the surrounding frame, designated F in FIG. 1, or other elements intended for engagement by the tab 10. The trigger lever spring 26 also functions to urge the trigger lever 12 in a counterclockwise direction to bring its tab into engagement with the web 2 or other similar functioning element forming a part of the latch assembly and the corresponding panel or door.

In the exercise of the present invention, the torque exerted by the bolt lever spring 22 is substantially greater than the trigger lever spring 26. It may be in the order of eight to thirty times as strong as the trigger lever spring. Prior to considering the operation of the flush latch, it is well to understand the operation of the conventional flush latch disclosed in the aforementioned patents. In the conventional construction, the extended end of the bolt lever 6 was merely doubled upon itself and therefore was in sliding frictional contact with the overlying end 21 of the trigger lever 12. Also, these springs were so arranged that the torque exerted on the bolt lever 6 was essentially the same as the torque exerted on the trigger lever 12. As a result, it was relatively easy to balance the forces if the adjacent ends of the two levers were brought into abutting relation. The exact point of balance or dead center varied somewhat with the configuration or geometry of the portions of the levers involved, and also the amount of force which might be applied to the tab end 10 of the bolt lever.

It has been found that if the force of the bolt spring 22 is in the range between eight and thirty times the force of the trigger lever spring 26, a balanced position cannot for practical purposes be attained. Instead, the bolt lever will tend to fly open rather than hang up and mislead the party installing the panel or door on which the flush latch is mounted. In the exercise of the present invention, the roller 20 minimizes the frictional loads so that even neglecting the force exerted by the bolt lever spring 22, a balanced or oncenter condition can be attained only with difficulty.

While in FIG. 3 the roller is shown as mounted on the bolt lever 6, a similar result is attained if a roller 31 is mounted under the end 21 of the trigger lever, as shown in FIG. 5. In this case, the bolt lever 6 is provided with an offset underlying extremity 32. Still further, as shown in FIG. 6, interengaging rollers corresponding to rollers 20 and 31 may be mounted respectively at the extended end of the bolt lever 6 and the overlying end 21 of the trigger lever 12.

In some instances, the coefficient of friction between the levers may be reduced by appropriate coating. In this case the bolt lever 6 may have a conventional offset extension 33 and then provided with a friction reducing coating 34. Depending upon the nature of the coating, the trigger lever may be provided with a coating 35. For example, the coating may be one of the well known carbon tetrafluorides.

In order to understand more fully the forces involved and therefore the need to minimize the frictional forces between the bolt lever and the trigger lever, and to determine the spring torques which are essential to dependable operation, reference is made to the following mathematical analysis and to FIGS. 8, 9,10 and 11.

With reference particularly to FIGS. 8 through 11, the following formula expresses the ratio of the force of the spring 22 on the bolt lever 6 t0 the force of the spring 26 on the trigger lever 12, or will minimize the area on the bolt lever end, where spring forces plus friction balance with the trigger lever partially engaged, such that a latch load on the bolt lever will open the latch.

It will be shown that, although a theoretical point, or small arc, of force balance is always possible, the optimum results obtained by using this formula, that for all practical purposes, to balance one ball bearing on another or the probability of attaining a balanced condition is extremely remote.

en s'r where:

M Moment of bolt spring force about pivot C (less friction of pivot C). M =Moment of trigger spring force about pivot B (less friction of pivot B). d=Horizontal distance from pivot C to D,

center of radius for the bolt end. r=Radius of bolt end from point D (roller or solid end). h=Horizont-al distance from pivot B to D. u= Coefficient of friction between bolt end and trigger surfaces (solid bolt end), or roller turning coefficient of friction. l= Distance from trigger pivot B, to start of trigger engaging surface, point A. 0= Angle measured counterclockwise from horizontal to line 1. m=Vertical distance from point B to point C.

0. f,=Horizontal component of f (resolved along line 1) through A. P=I:Iorizontal component of F (resolved along line I) through A. Y=Vertieal distance of point A above point D at any 0.

NOTES:

1. Point B must always fall left of, or directly under point D, (h **O) otherwise bolt loads(F) will urge trigger clockwise and open even at 6 the locked position. Making h=0 is considered bad practice. Tolerances can throw Bright of D.

2. The vertical displacement of pointD from 6, to 6 is less than r, which is very small compared to d (about one to nine in smallest of normal designs). We may normally ignore the extremely small horizontal displacement ofpoint D from 6, to 0 and will do so in deriving our spring ratio formula.

3. 3. A, must travel along are A, about point B, to release the bolt. Point D, on the bolt interlocking end, must move downward from 9,, to 9 travel of the trigger. If point D moves downward, the latching end of the bolt lever 6must move upward, effectively increasing the latch load. Therefore, this trigger-bolt interlock design provides an ovcrcenter safety lock.

4. The greater is load F, the greater the counterclockwise. locking moment placed on the trigger. At dead'center (0,) the trigger spring should be strong enough to overcome friction, carrying the trigger on to 6 While the latch could theoretically withstand its ultimate load with thetrigger dead center (6, it would be considered bad practice. impact or vibration might shift this delicate balance in a lightly loaded latch.

5. Good practice would suggest the friction force (0 6,) be computed as the resultant of both the bolt spring moment, and the maximum load on the latch bolt obtainable in latching the bolt. For hand operation the maximum closing force on the bolt is designed for 20-30 pounds. The relatively heavy spring ofthe bolt, used to urge the bolt past the trigger from 0 0 need only act through a very small angle of bolt travel (until the trigger approaches 6 A lighter auxiliary spring may then be used to urge the bolt onward to a flagging position indicating the latch is unlatched.

(2.) Derivation of l, d, r,m, h, (9)

(3.) 0 cos- To find an expression for the horizontal component of friction fr:

sin (1800a) "a 1: (b.)f1 41' tndfr fr Sing from law of since sin 0 To find an expression. for the horizontal component of bolt force P:

(8.) P=F sin a- For the bolt to rotate past the trigger, P fr and:

(10') (P-fr')l sin 0 MS Substituting'for P and fr sin (0 +cos T p i h t [l cos y co 0 r Sine Rearranging the previous formula:

lsin 0 yd- (1 cos 13-h) (1 sin 6my) uT' sin 6+cos sin 6 Usefnl relationships from the theory evolved above:

(13.) Ma where P=f,, and

To permit the trigger spring to overcome friction at 0 and close:

This will establish an upper limit for the ratio for the. %rlpbined bolt M, of bolt spring and latch load.

ere:

(15.) Q0=yd (loos 0-h) (1 sin 8-m-y) In applying the above formulas and equations, it has been found that a practical latch may be made if the ratio between the bolt lever spring and the latch lever spring be in the range between 8 to l and 30 to l, and that the coefficient of friction (p) be between 0.4 and 0.01.

A latch in which one or both of the contacting surfaces are coated with a carbon tetrafluoride FIG. 7) reduces the sliding friction to about 0.10; whereas, a single roller construction (H65. 3 and 5) reduces it to about 003 and a double roller (FIG. 6) reduces it to about .02.

Reference is now directed to FIG. 12. In this construction, shown more fully in U.S. Pat. No. 2,721,750, a channelshaped trigger lever 33 is fitted within an aperture provided in a channel-shaped handle lever 34. The trigger lever is pivotally mounted on a pivot pin 35 extending through its, side flanges and into the side flanges of the handle lever.

The handle lever 34 is pivotally mounted near one end on a fixed journal pin 36, and is connected by a link 37 to a bolt 38.

The flanges of the trigger lever are notched at one side below the pivot pin 35 to form hooks 39, the upper edges of which function in the manner of the under surface 21 of the first described structure. The upper edge of each hook engages a keeper pin 40 having a roller 41 corresponding to the pin 19 and roller 20 of the first described structure.

The handle lever 34 is urged outwardly by a handle lever spring 42 wrapped about the journal pin 36 and corresponding to the spring 22 of the first described structure wrapped about the pin 11. The trigger lever 33 is pivoted toward its latched position by a trigger spring 43 wrapped about the pin 35 corresponding to the spring 26 and pin 17 of the first described structure.

Reference is directed to FIG. 13. The latch here illustrated is shown more fully in U.S. Pat. No. 2,712,955 and is insofar as p the present invention is concerned essentially the same as FIG.

12 except that a second journal pin 44 carries a latch hook 45 and receives the handle lever spring 42. Also the latch hook 45 extends around the pin 36 under the trigger lever and the pins 40 and rollers 41, engaged by the two hooks 39, may be carried by the latch hook 45.

Reference is directed to FIG. 14. This construction, more fully disclosed in U.S. Pat. No. 2,833,582, includes a handle lever 46 which is mounted on a shaft 47 for translatory and rotary motion. The shaft 47 is urged axially by a spring 48 corresponding to the spring 22 of the first described structure. The handle lever 46 is provided with a trigger lever 33 which is pivoted about a pin 35 and engages the pivot pin 40 having a roller 41 and pivoted by a trigger spring 43.

The relation of the hook or hooks 39 of each of the structures shown in FIGS. l2, l3 and 14 to the pin 40 and its roller 41 is essentially the same as the relationship of the end surface 21 and the roller 20 as is indicated by comparison of FIGS. 9 and 15. That is, the formula developed for the first described structure is applicable to the structures shown in FIGS. 12, 13 and 14. For convenience of comparison, the same data is applied to FIGS. 12,13 and 14, as appears on FIG. 8. In the construction shown in FIG. 14, M=O and M,.,,=Fd.

While particular embodiments of this invention have been shown and described, it is not intended to limit the same to the details of the constructions set forth, but instead, the invention embraces such changes, modifications and equivalents of the various parts and their relationships as come within the purview of the appended claims.

lclaim:

1. A latch adapted to be flush mountedwithin a slot provided in a panel set within a surrounding frame, said flush latch comprising:

a. a bolt lever pivotally mounted within said slot, said bolt lever including a latch end engageable with said frame to secure said panel, a retained end, and an intermediate portion disposed flush with said panel when said bolt .lever is in its latched and secured condition and disposed in angular relation with said panel when said bolt lever is in its unlatched condition;

b. a trigger lever pivotally mounted in said slot in tandem relation with said bolt lever, said trigger lever having its pivotal point under the retained end of said bolt lever and including a retaining end overlying the retained end of said bolt lever when said latch is in its secured condition, a tab end underlying a margin of said panel slot. and an intermediate portion disposed flush with said panel when said trigger lever is in its engaged condition and disposed in angular relation with said panel when said trigger lever is in its disengaged condition;

c. a bolt spring for applying torque forcing the retained end of said bolt lever against the retaining end of said trigger lever, and tending to turn said bolt lever toward its unlatched condition;

d. a trigger spring for applying torque to the retaining end of said trigger lever to move said end over the retained end of said bolt lever and said tab toward a margin of said slot;

e. the retained end of said bolt lever and the retaining end of said trigger lever being urged by said springs into mutual engagement at a point, when said latch is secured, producing a resulting force tending to urge said levers toward their latched and engaged conditions, said bolt and trigger levers being movable from said mutually engaged position past a mutually abutting position to their respective unlatched and disengaged conditions in opposition to the friction produced between the mutually engaged portions of said levers and the force of said trigger spring;

f. the torque applied by said bolt spring being sufficiently higher than the torque applied'by said trigger spring as to cause said lever to snap to its open position as said levers approach their mutually abutting positions; and

g. means providing a lower coefficient of friction between the mutually engageable portions of said bolt and trigger levers than that of the material of said elements.

. A flush latch, as defined in claim 1, wherein:

. the torque ratio of said bolt lever spring to said trigger spring being defined by the formula:

b. the coefficient of friction between the retained and retaining ends of said levers is less than a function of:

loos 0hy cot 0- sin 0 b. where:

T loos 0h) c. and a is not greater than Ms Zr 7. The combination with a latch of the type including a handle lever, a pivotable trigger lever movable between a latched position and an unlatched position and means engaged by said trigger lever to secure said trigger lever in its latched position, said trigger lever and said means having mutually engaging elements which move past a mutually restraining condition in a pivotal movement of said trigger lever between a latched condition and an unlatched condition, of means for minimizing said mutually restraining condition between said elements,

comprising:

a. a first spring for applying a torque to said handle lever in a direction tending to interlock said mutually engageable elements;

b. a second spring for applying a torque to said handle lever tending, on movement of said trigger lever toward its unlatched condition, to force said mutually engageable elements in a direction to effect disengagement of said elements;

. the torque applied by said second spring being substantially higher than the torque applied by said first spring thereby creating an unstable relation between said elements when said elements are in their mutually restraining condition whereby said trigger lever snaps toward its latched position or its unlatched position; and

d. means establishing a lower coefficient of friction between said mutually engaging elements than that of the material of said elements.

8. A latch, as defined in claim 7, in which a common frame pivotally supports said handle lever and said trigger lever, said handle lever includes a bolt end, and said levers overlap to form said mutually engageable elements.

9. A latch, as defined in claim 7, in which a frame pivotally supports said handle lever, a bolt is operatively connected with said handle lever, and one of said mutually engageable elements is fixed with respect to said frame 10. A latch, as defined in claim 7, in which a frame pivotally supports said handle lever, a bolt is operatively connected with said handle lever, and one of said mutually engageable elements is carried by said bolt.

11. A balanced force minimizing means for flush latches, as defined in claim 7, wherein the coefficient of friction established by said low friction means is less than 0.4.

12. A balanced force minimizing means for flush latches, as defined in claim 7, wherein said low friction means is a roller carried by one of the mutually engaging elements.

13. A balanced force minimizing means for flush latches, as defined in claim 7, wherein said low friction means is a pair of rollers carried by both of the mutually engaging elements.

14. A balanced force minimizing means for flush latches, as defined in claim 7, wherein said low friction means is a coating ofa friction reducing media on at least one of the mutually engaging elements.

15. A balanced force minimizing means for flush latches, as defined in claim 7, wherein:

a. the relationship between said mutually engaging elements and said springs is expressed in the following equation:

M81319 2 (l sm 0) yd-(l cos 0h)(l sin 6my) r sin (ti-l-cos 1 cos 0-h-y cot 0 9 b. where:

Z w/'r (Z cos 0-h) c. and a is not greater than 

